Formation of Recycled Pulsars in Common Envelope Binaries
Published in The Astrophysical Journal, 2026
Key Information
- Authors: Yu-Dong Nie, Yong Shao, Jian-Guo He, Ze-Lin Wei, Shi-Jie Gao, Xiao-Jie Xu, Xiang-Dong Li
- Journal: The Astrophysical Journal
- Year: 2026
- DOI: 10.3847/1538-4357/ae3569
- NASA ADS: 2026ApJ…997..265N
- arXiv: 2601.04355
Abstract
We present a systematic study of the evolution of low- and intermediate-mass X-ray binaries consisting of a 1.4 M⊙ neutron star (NS) and a donor star of mass 1─8 M⊙. Using grids of detailed MESA simulations, we show that for donor masses of 2─8 M⊙, mass transfer may be dynamically unstable, leading to a common envelope (CE) phase. By adopting CE ejection efficiencies in the range αCE = 0.3─3.0, we find that post-CE binaries frequently experience a CE decoupling phase (CEDP), which plays a critical role in determining their final orbital and compositional properties. Systems with initial donor masses ≳3.5 M⊙ predominantly evolve into NS binaries with carbon─oxygen or oxygen─neon white dwarfs (WDs) with masses between 0.5 and 1.4 M⊙. Comparison with the observed population of binary pulsars with a WD companion shows better agreement with higher CE ejection efficiencies (αCE = 3.0). Furthermore, we demonstrate that NSs can accrete a sufficient amount of matter (≳0.01 M⊙) during the CEDP and subsequent Case BA/BB/BC mass transfer phases to be effectively recycled into millisecond pulsars. We identify two distinct evolutionary channels capable of reproducing the observed characteristics of the millisecond pulsar PSR J1928+1815 with a helium-star companion. Our results highlight the importance of the CEDP in the formation of recycled pulsars and provide constraints on the CE ejection efficiency during binary evolution.